Binders are employed in many ceramic compositions to provide the requisite green strength and plasticity for the shaping of the ceramic article prior to firing. Generally, the binder should volatilize readily, leaving essentially no residual ash during the firing, and ideally this decomposition should occur at less than 400.degree. C. Furthermore, for certain purposes, binders should also volatilize and degrade cleanly in a nonoxidizing atmosphere, e.g., nitrogen, so that oxidizable metals such as copper, for example, will not oxidize during the fabrication of articles containing such metals, e.g., multilayer thick film circuits. In addition, it is advantageous for the binder to require little or no external plasticizer.
To obtain binders having such desired properties, extensive research on polymers has been conducted during the past fifty years. For example, in the past, various polymeric materials have been employed as the binder for green tapes, e.g., poly(vinyl butyral), poly(vinyl acetate), poly(vinyl alcohol), cellulosic polymers such as methyl cellulose, ethyl cellulose, hydroxy ethyl cellulose, methylhydroxy ethyl cellulose, atactic polypropylene, polyethylene, silicone polymers such as poly(methyl siloxane), poly(methyl phenyl siloxane), polystyrene, butadiene/styrene copolymer, polystyrene, poly(vinyl pyrrolidone), polyamides, high molecular weight polyethers, copolymers of ethylene oxide and propylene oxide, polyacrylamides, and various acrylic polymers such as sodium polyacrylate, poly(lower-alkyl acrylates), poly(lower alkyl methacrylates) and various copolymers and multipolymers of lower alkyl acrylates and methacrylates. Copolymers of ethyl methacrylate and methyl acrylate and terpolymers of ethyl acrylate, methyl methacrylate and methacrylic acid have been previously used as binders for slip casting materials.
Representative references to polymeric binders are as follows:
U.S. Pat. No. 2,952,877 discloses a method of making ceramic a substantially water-soluble polymeric organic binder and a substantially water-soluble compatible organic plasticizer for said binder, with polyvinyl alcohol and triethyethylene glycol being preferred. Other binders are hide blue, alkali casein, dextrin, starch adhesives, polyacrylic acids, and polyacrylamide.
U.S. Pat. No. 2,966,719 discloses a compatibly plasticized thermoplastic binder resin, a preferred binder composition containing polyvinyl butyral (binder), polyalkylene glycol derivative (plasticizer), and an alkyl ether of polyethylene glycol (wetting agent). This patent also teaches how to manufacture thin ceramic films which may be handled in the same manner as tapes.
JP 62-230664 discloses the use of an isobutyl methacrylate copolymer with other vinyl monomers, having a glass transition temperature (T.sub.g).ltoreq.40.degree. C. as a binder for ceramics. The use of this binder is said to minimize carbon retained in the fired ceramic thereby eliminating cracking and fissures in the ceramic product.
U.S. Pat. No. 4,613,648 discloses the use of an organic medium for the dispersion of inorganic solids containing as a binder a mixture of compatible polymers of methacrylates, acrylates, and an ethylenically unsaturated acid, said polymer having an M.sub.w /M.sub.n no greater than 5.5. The T.sub.g of the polymer (and plasticizer therein, if any) is -30.degree. to +45.degree. C.
U.S. Pat. No. 4,655,864 discloses a polymeric binder selected from poly(.alpha.-methylstyrene) and polymers of methacrylate, for which the glass transition temperature of the polymer, including any plasticizer therein, is between -30.degree. and +20.degree. C. The binders are effective for nonoxidative firing in that they burn cleanly and thoroughly when fired at 825.degree. to 1025.degree. C.
Air products and Chemicals, Inc.; Product Information Bulletin discloses the use of poly(alkylene carbonates) for binders in ceramic applications. Poly(propylene carbonate) is said to differ from other ceramic binders in that it decomposes completely in air by 300.degree. C. and by 360.degree. C. in nitrogen. The glass transition temperature of the latter polymer is +40.degree. C.
Irrespective of the vast research that has been conducted, there is still a need for improved or alternative binders for the production of ceramics, and especially for the production of ceramic tapes.